Overview
ISO 14502-1:2005 defines a validated colorimetric method using Folin‑Ciocalteu reagent for the determination of the total polyphenol content in green and black teas, including leaf teas and instant tea. The method specifies sample preparation, extraction, reagent composition and calibrations so laboratories can produce comparable, quality-controlled polyphenol data for tea products.
Key topics and technical requirements
- Scope: Applicable to leaf and instant teas (green and black tea products).
- Principle: Polyphenols are extracted and react with Folin‑Ciocalteu reagent to form a blue chromophore measured spectrophotometrically (maximum absorbance ~765 nm).
- Extraction:
- Leaf tea: extracted with 70% methanol at 70 °C (two sequential extractions combined).
- Instant tea: dissolved in hot water with 10% acetonitrile added to stabilize the extract.
- Reagents and calibration:
- Use analytical‑grade solvents (methanol, acetonitrile) and Folin‑Ciocalteu phenol reagent (diluted to 10% for assay).
- Gallic acid stock and dilute standards (nominal 10–50 µg in assay) are used to construct a linear calibration graph.
- Instrumentation and parameters:
- Spectrophotometer set at 765 nm, 10 mm cells.
- Centrifugation, vortex mixing and controlled water bath at 70 °C are specified.
- Assay procedure: Defined aliquots, reagent addition timing (3–8 min window), sodium carbonate development and 60 min color development before measurement.
- Calculations & quality: Calibration slope/intercept used to quantify polyphenols; the standard includes precision data (repeatability and reproducibility) and reporting requirements.
Applications and users
- Food testing laboratories performing routine quality control and specification testing for tea products.
- Tea manufacturers and processors monitoring polyphenol content for product development, labeling and process control.
- Regulatory bodies and standards organizations requiring harmonized test methods for ingredient composition and claims.
- Research institutions studying antioxidant content, cultivar comparisons or processing effects on tea polyphenols.
Practical benefits include reproducible total polyphenol data for product specification, shelf‑life studies, provenance/authenticity checks and nutritional labeling when combined with appropriate sampling procedures.
Related standards
For implementation, laboratories should obtain the full ISO 14502-1:2005 text from ISO or national standards bodies to follow exact procedural details and reporting requirements.
Open preview (PDF)Determination of substances characteristic of green and black tea — Part 1: Content of total polyphenols in tea — Colorimetric method using Folin-Ciocalteu reagent
